Thrombospondin‐1 expression may be implicated in liver atrophic mechanism due to obstructed portal venous flow

Aim Liver is an amazing organ that can undergo regenerative and atrophic changes inversely, depending on blood flow conditions. Although the regenerative mechanism has been extensively studied, the atrophic mechanism remains to be elucidated. Methods and Results To assess the molecular mechanism of liver atrophy due to reduced portal blood flow, we analyzed the gene expressions between atrophic and hypertrophic livers induced by portal vein embolization in three human liver tissues using microarray analyses. Thrombospondin (TSP)‐1 is an extracellular protein and a negative regulator of liver regeneration through its activation of the transforming growth factor‐β/Smad signaling pathway. TSP‐1 was extracted as the most upregulated gene in atrophic liver compared to hypertrophic liver due to portal flow obstruction in human. Liver atrophic and hypertrophic changes were confirmed by HE and proliferating cell nuclear antigen staining and terminal deoxynucleotidyl transferase‐mediated digoxigenin‐dUTP nick‐end labeling. In an in vivo model with portal ligation, TSP‐1 and phosphorylated Smad2 expression were continuously induced at 6 h and thereafter in the portal ligated liver, whereas the induction was transient at 6 h in the portal non‐ligated liver. Indeed, while cell proliferation represented by proliferating cell nuclear antigen expression at 48 h was induced in the portal ligated liver, the sinusoidal dilatation and hepatocyte cell death with terminal deoxynucleotidyl transferase‐mediated digoxigenin‐dUTP nick‐end labeling was detectable at 48 h in the portal ligated liver. Conclusions Obstructed portal flow induces persistent TSP‐1 expression and transforming growth factor‐β/Smad signal activation in atrophic liver. Thrombospondin‐1 may be implicated in the liver atrophic change due to obstructed portal flow as a pro‐atrophic factor.